Ok I have a serious project on my hands.

It is a big project will take me probably a full year and then some to complete. To sum it all up real quick and short, I am getting a 1985 C-30 dually dump truck 2 wheel drive with a blown 350 in it standard trans 4:11 ratios for free. What I want to do to it using parts from friends and keeping it cheap, is turn it into a 4x4 diesel. I want to change it into a 6.2L Turbo charged 4x4 with 3:73 ratios and a 5 speed trans. I read the article about the army pickup and I think I'm going to go with the NV4500 trans like you guys did. I am unsure about a transfer case right now but I'm doing some research. I basically want to keep the low end with some decent torque  and be able to carry somewhat of a load around town. But yet I want to get some decent mileage out of it. Thats why  Iwant the 5 speed with the 3:73s I figure that would more than suffice. One of my buddies has a 91 chevy with a 5 speed 3:73s 4x4 dump truck and he gets awesome mileage with it. He can tow his landscape trailer and have a load on it and it really doesnt bother it. So I was wondering what kind of insight some of you mechs here might have to say about it. I know its a huge project, my dad being a diesel mechain and all that stuff thinks its a dumb project and I'll never get it done but its what I want.  Hope to hear some kind of feedback from you guys.

~ray from Connecticut.  

You are going about this a bit wrong. For one you are going wrong way on gear ratio. You need to go to a 4.56 or better in that chassis with a 6.2. A 6.2 is weaker than a 350 even turbo charged but it does use less fuel. Also you have to be real careful about turbo charging a 6.2 as heads are not very strong nor designed for turbo charging. The 6.5 is basically a improved 6.2 with a stronger block and heads and designed to take some boost. Also IDI engine like 6.2 do not respond very well to boost anyway and you get less return as you raise boost level. This is one reason why Detroit went to DI engines because they respond so much better to boosting. BTW I have drive 1 ton in years past with 6.2's and 4.56's and it is a nice marriage. They run well for HP and get decent MPG. This is one engine that you do not want to lug if you expect it to pull well and last. Pre chamber IDI engines like this do best in their upper not lower RPM ranges.  

Ok that at least makes sense to me. I did do some research on the 6.2 and Banks offers a turbo that they say was offered stock on new 6.2L diesels in the 80s, so I figured I would go with that and I wouldnt have to change anything to the block or heads if it was offered as standard equipment. They even showed a video on the website about it. And I do get why it works better in the upper RPM's because it is like the old detroits like the 71's and 53's series' engines where they have to be screamin to be working good. Why is 4:56 ratios better in this case? Just wondering.  

It is because it is a pre-chambered engine. (fuel is injected into a separate chamber and it burns and expands in piston area via a orfice between them. This changes the best RPM for them with lowest fuel usage per Horse Power Hour delivered. IDI engine also have much higher CR's too. Usually in the range of 21 to 23 to 1. You want to wind the engine up some as it is quite happy at 3000 or even 3500 RPM (unlike other motors you mention) 6.2's and 6.5's do their best when you kinda run them like a gas motor and like them wind up some and not lug them. (hence deep gears) Unlike DI engines, IDI engine have much broader usable torque/RPM range. BTW, if you boost it I would limit boost on a 6.2 to about 7 PSI or so because heads are not designed for it. YOu are not going to hurt a 6.2 reving it up some but you can forcing it to operate at a lower RPM under load. THis is not a DI engine that does its best at lower RPM's and do not treat it as such in this vehicle and it will do well.  

well i really think you need to dicth the 6.2 idea and go with a 6.5 and but some of the banks stuff on there....you will be much happier and powerfull too...on the gear ratios itd be nice to know what size tires your planning on running but from your description im guessing its gonna be pretty close to stock....  
Solid axle chevys can't be beat!
My dream truck: 73-91 chevy 3500 crew cab srw with dana 60/14bolt, 6 inc long travel lift with KING shocks, 37 inc tires and a 24v cummins diesel, nv5600 and np205

IDI engine like to wind up because it has to do with when piston travels down quicker with higher RPM's you get a better burn and expansion from pre-chamber down in to piston area in the more rapidly expanding space so more energy is transfer before gasses are cooled by contact with prechamber walls and loose some efficiency and power.  

ya they are going to be stock tires. It seems to me going with bigger tires on duallies gets more expensive faster. I believe they are the 245/75R16s I think. Havent checked in awhile.  

Stock dualie tires should be 215 or 235/85's  

Okay I so I might as well tell you this since I Know about it.One of my buddys parting out/selling a 82 6.2 turbo blazer.It has a 44 in the front a 700r4 tranny and every thing.I dont no what state your in and the 44 is a little light for the truck but what the heck.He'll probly take 150 for the axel or 500-600 for the truck.It does run good but needs a water pump and is rusty.  
Dying ain't much of a livin'
From my favorite movie.
Trucks...
1989 150(200k) 33 inch hawgs and a blown 302.
1995 Pathfinder(178k)and still going with 31s.
Bikes.
2004 Yamaha TTR 225,barly used.
Kawasaki 750 (26k) Not ran right since carbs rebuilt.
!972 Yamaha mini enduro.The niceest one I've ever seen thats never been painted.
New 2002 f150,fx4,5.4v8,after market tranny coolers and unirol tires.